Paint the House Black! (0.5.7 Alpha)

The most visible changes are that pure black is now an allowed paint color and the paint scraper now removes Alpha paint.

This release also fixes a number of bugs and includes some internal engine improvements. Memory usage on creation of a new world and during loading are now much slimmer, allowing larger worlds to be used without hitting an OutOfMemoryError from Java. I believe I've also fixed a deadlock issue that was very, very rarely causing the game to freeze (I've only ever seen this bug twice).